The disclosure relates to fuel delivery systems and pumps employed to circulate fuel through filter assemblies.
Lift pumps are low-pressure supply pumps that transmit fuel to a high-pressure pump. In most fuel supply systems for diesel internal combustion engines, electric motor-driven lift pumps are used to push or pull fuel through filter assemblies and deliver a specified volume of clean fuel at a specified pressure to downstream fuel system components such as high pressure pumps feeding fuel injection systems. Lift pumps may be incorporated into fuel filter assemblies or arranged separately. Most prior art lift pumps are driven by simple DC motors having a constant output, resulting in fuel flow at a constant rate. It is common for prior art fuel delivery systems to employ a mechanical regulator to control output pressure, which adds to the complexity and cost of the assembly. Some more recent lift pumps have been driven by brushless DC motors, which are more complex and expensive but provide increased reliability and the ability to control the output of the pump by varying power delivery to the motor.
Heat dissipation is an issue in both brushed DC and brushless DC motor-driven pump designs, with the fuel being pumped commonly serving as coolant for both the motor and any electronic components associated with an electronic controller used in conjunction with brushless DC motors. Most pumps of this type employ a “wet” configuration where the motor and/or controller are bathed in fuel as it is pumped through the assembly.
The consumption of fuel by an internal combustion engine varies widely, depending upon operational demands. In the absence of the ability to vary the rate of fuel delivery, the pump associated with a fuel delivery system must be operated at a constant fuel delivery rate sufficient to satisfy maximum engine demand for fuel. One result is that under most engine operating conditions, more fuel is delivered to the engine than is used, with excess fuel being returned to the fuel reservoir. Recirculated fuel is typically heated by passage through the fuel delivery system, and can potentially pick up particulates and contaminants that are returned to the fuel reservoir.
Brushless DC motors can overcome the reliability issues associated with brushed DC motors and present unique opportunities to control the speed and torque of the motor.
There is an opportunity to employ brushless DC motors in a fuel delivery system to match fuel delivery to engine demand and minimize the volume of fuel recirculated in such systems.